[Gluster-devel] Gluster AFR volume write performance has been seriously affected by GLUSTERFS_WRITE_IS_APPEND in afr_writev

[Pranith Kumar Karampuri]

Sorry for the delay in response.

On 01/15/2016 02:34 PM, li.ping288 at zte.com.cn wrote:
> GLUSTERFS_WRITE_IS_APPEND Setting in afr_writev function at glusterfs 
> client end makes the posix_writev in the server end  deal IO write 
> fops from parallel  to serial in consequence.
>
> i.e.  multiple io-worker threads carrying out IO write fops are 
> blocked in posix_writev to execute final write fop pwrite/pwritev in 
> __posix_writev function ONE AFTER ANOTHER.
>
> For example:
>
> thread1: iot_worker -> ...  -> posix_writev()   |
> thread2: iot_worker -> ...  -> posix_writev()   |
> thread3: iot_worker -> ...  -> posix_writev()   -> __posix_writev()
> thread4: iot_worker -> ...  -> posix_writev()   |
>
> there are 4 iot_worker thread doing the 128KB IO write fops as above, 
> but only one can execute __posix_writev function and the others have 
> to wait.
>
> however, if the afr volume is configured on with storage.linux-aio 
> which is off in default,  the iot_worker will use posix_aio_writev 
> instead of posix_writev to write data.
> the posix_aio_writev function won't be affected by 
> GLUSTERFS_WRITE_IS_APPEND, and the AFR volume write performance goes up.
I think this is a bug :-(.
>
> So, my question is whether  AFR volume could work fine with 
> storage.linux-aio configuration which bypass the 
> GLUSTERFS_WRITE_IS_APPEND setting in afr_writev,
> and why glusterfs keeps posix_aio_writev different from posix_writev ?
>
> Any replies to clear my confusion would be grateful, and thanks in 
> advance.
What is the workload you have? multiple writers on same file workloads?

Pranith
>
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